Maximum lowest temperature for Japanese Maples

ajm55555

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In the ground, acer plamatum will survive in zone 5 (-20F), but the need to be well protected from drying winds.
Roots in a pot are only good to about 15F. You can set the pot on/in the ground and heavily mulch if you don't have indoor protection.
Thank you for the information and the link 0soyoung. Precious!
 
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There are many factors that determine the results, so don't assume numbers are accurate. Also, no one can honestly tell you a minimum temperature and length of time. There are guidelines, like USDA zone info, but they are not to be taken as gospel. The single most important factor is the health of the tree.
My experience is that a 24-48 dip into single digit or negative number temps is less harmful than a constant 12 hour repeated freeze/thaw cycle.
 

ajm55555

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I'll go through 10-15 days with minimum temperatures in the low 10s and mid 20s during the day.
Should I take precautions?
I can bring them inside in a non heated but full of light part of the house.
 

GGB

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WTH is going on in Delaware? it's been like 40 degrees everyday in SE Pennsylvania. I'm zone 6B and don't give my JM any winter protection but it also grew as a seed here (many years ago) from a tree that thrived here. So I think sometimes it's about genetics
 

JudyB

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I would not bring your tree inside where there is lots of light. You want to keep it dormant. Dormant trees don't need light, and light causes heat. Do you have an unheated garage?
 

j evans

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It has been that cold here off and on for weeks. Mine are in the ground behind the garage and seem to do fine there as a general rule. But there is always that one time, spring, got anxious, pulled pot up, fine for a week then one night........freeze ooooo and that one was a popsicle just from one cold night.
 
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I'll go through 10-15 days with minimum temperatures in the low 10s and mid 20s during the day.
Should I take precautions?
I can bring them inside in a non heated but full of light part of the house.
10-15 days with those temps shouldn't bother a healthy japanese maple. Don't bring them indoors unless its into a cold room with minimal light. You can kill them with kindness, and many do.
You should post pictures of the trees which are the subject of your request for advice. You will get more accurate advice if people know what they are actually advising you on. Its not one size fits all, unfortunately.
 

ajm55555

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I would not bring your tree inside where there is lots of light. You want to keep it dormant. Dormant trees don't need light, and light causes heat. Do you have an unheated garage?
I know, there's too much light there but I don't have a garage. Temps are in the 50s there and I don't know if the combination of these temperatures and the light would wake them up.
 

ajm55555

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Winters here in Southern Germany are cold but there can be periods of relatively warm weather with day temperatures in the 50s. My deciduous trees are in full sunlight but never showed signs of waking up in the middle of Winter. I'm really convinced that besides temperature and light there are other factors that might convince a tree it's Spring, like length or daylight and others that I can't think of now.
For this reasons my only worry is if the trees can sustain relatively deep freeze for a couple of weeks.
From your answers, I guess I'm fine leaving the JM outside because the temperature is not too low and the swings do not lead to cycles of freezing up and melting down, which could be more harmful to the roots than prolonged freezing.
Thanks for your insight!
The tree (sorry for the blurred pic) this morning at 16F20170120_084901.jpg
 

JudyB

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I know, there's too much light there but I don't have a garage. Temps are in the 50s there and I don't know if the combination of these temperatures and the light would wake them up.
Yes these are the exact conditions that can break dormancy.

If that tree is up on a bench then you can do better than that for protection outside. Even just on the ground is a better protection than being up off the ground. You can mulch and if you prepare next time, you can dig them in and then mulch. You can wrap frost cover around them for wind protection as well.
 

ajm55555

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Yes these are the exact conditions that can break dormancy.

If that tree is up on a bench then you can do better than that for protection outside. Even just on the ground is a better protection than being up off the ground. You can mulch and if you prepare next time, you can dig them in and then mulch. You can wrap frost cover around them for wind protection as well.
What I thought is that if it sits on the bench it's closer to the house and better protected against the cold and wind. I'll wrap it with paper and put some mulch on top. Thanks for the tip Judy.
 
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Judy is correct about placing the tree on the ground. One thing that does is minimize the temperature fluctuations. The ground will stay a more consistent temperature than your bench, and your tree is less likely to dry out while sitting on the ground. Put your tree on the ground in the shade.
The roots/soil can freeze and stay frozen. Don't be scared.
Length of daylight hours does affect dormancy.
 

ajm55555

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Judy is correct about placing the tree on the ground. One thing that does is minimize the temperature fluctuations. The ground will stay a more consistent temperature than your bench, and your tree is less likely to dry out while sitting on the ground. Put your tree on the ground in the shade.
The roots/soil can freeze and stay frozen. Don't be scared.
Length of daylight hours does affect dormancy.
Thanks Judy and Don. I will do this and not worry until I see a polar bear knocking at the door ;-)
 

ysrgrathe

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As @0soyoung noted the critical temperature is 15-16F (-9C) for roots: if the roots fall below that, they die. How long it takes in -9C weather for the roots to hit -9C depends on the location, light, wind, size of pot, etc. When Judy/Don say to put it on the ground, you'll find it acts like a giant heat sink regulating the temperature which can buy you a lot more safety margin when temps dip below -9C.

Beyond that: different cultivars are more or less sensitive. I have had poor luck with coral barks in zone 6.
 

Solange

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One thing I thought of not mentioned here - Early morning sun can be bad. If the tree is nice and frosty and that sun hits it, thawing it quickly, that's bad. Slower fluctuations are better.
 
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One thing I thought of not mentioned here - Early morning sun can be bad. If the tree is nice and frosty and that sun hits it, thawing it quickly, that's bad. Slower fluctuations are better.
That's why I said to put the tree on the ground in the shade. There is a reason northern farmers paint tree trunks white.
 
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As @0soyoung noted the critical temperature is 15-16F (-9C) for roots: if the roots fall below that, they die.
My experience is not consistent with that statement. I have japanese maples in lower temperatures for long periods of time and they do not die. There are many other factors than temperature.
 

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